1. Field of the Invention
This invention relates to a fuel injection timing control system and method for a direct injection type internal combustion engine, which is preferable for a spark ignition type four-cycle internal combustion engine.
2. Description of Related Art
Conventionally, a direct injection engine, that injects fuel from a fuel-injecting valve (injector) directly into a cylinder, performs fuel injection during an intake stroke to uniformly mix air and the fuel in the cylinder when a medium load is applied to the engine. If a fuel injection starting timing is early in the intake stroke, a fuel spray collides with the top of a piston to form a fuel film at the top of the piston. This causes a relatively large amount of smoke and HC to be outputted.
If a fuel injection ending timing is late, the fuel spray partially adheres to an inner wall of the cylinder and is absorbed by oil on the inner wall of the cylinder. The absorbed fuel is scraped off by the piston without evaporating. This results in the dilution of oil.
This tendency is striking when an engine is so cold as not to promote evaporation of the fuel.
For the reasons stated above, the direct injection engine needs to perform the fuel injection at a certain limited crank angle when injecting the fuel in the intake stroke. Limiting the fuel injection period in this manner prevents generation of smoke and HC, and the dilution of oil.
If the fuel, corresponding to an intake air volume, is injected while a high load is being applied to the engine (e.g. in a full throttle operation), however, it is impossible to inject all the fuel at the above-mentioned crank angle because the engine is revolving at a high speed. In this case, generation of smoke and HC, and dilution of oil are unavoidable.
Further, if the fuel injection period is limited to such a predetermined period (within the crank angle) as to avoid generation of HC and smoke, and the dilution of oil when the fuel is being injected during the intake stroke, the fuel runs short because the predetermined period varies according to the operational status of the engine.
It is, therefore, an object of the present invention to provide a direct injection type internal combustion engine capable of properly setting a timing for permitting the fuel injection during the intake stroke to thereby prevent generation of HC and smoke, and the dilution of oil.
To attain the above object, the present invention provides a fuel injection timing control system for a direct injection type internal combustion engine capable of switching a fuel injection mode according to an operational status between a compression stroke injection mode for performing fuel injection mainly during a compression stroke and an intake stroke injection mode for performing fuel injection mainly during an intake stroke, the fuel injection timing control system comprising: a correcting unit that corrects a fuel injection timing in the intake stroke according to parameters representing a tendency of fuel to adhere to an inside of the internal combustion engine, wherein when a fuel injection volume required during the intake stroke injection mode cannot be injected within the fuel injection timing corrected by the correcting unit, the correcting unit sets a timing for injecting remaining fuel during a compression stroke following the intake stroke in one combustion cycle to satisfy the required fuel injection volume; and a control unit that controls injection of fuel into the internal combustion engine according to the fuel injection timing corrected by the correcting unit; wherein the correcting unit detects a temperature relating to the internal combustion engine as a parameter representing the tendency of the fuel to adhere to the inside of the internal combustion engine, and corrects the fuel injection starting timing in said intake stroke to retard side as the detected temperature becomes lower.
This fuel injection timing control system for the direct injection type internal combustion engine reliably prevents generation of HC and smoke, dilution of oil, increases power, and improves fuel economy without increasing cost and weight by a simple structure wherein the fuel injection timing in the intake stroke is corrected according to the parameters representing the tendency of the fuel adhering to the inside of the internal combustion engine. Further, the fuel injection timing control system corrects the fuel injection starting timing in the intake stroke to a retard side as the detected temperature becomes lower. This effectively prevents the generation of HC and smoke, and the dilution of oil, when, for example, the engine is cold started.